Variable resistance



May 4,1926.

' T. APPLEBY VARIABLE RESISTANCE Original Filed March 23, 1920 INVENTOR.

CBM 4 ATTORNEY.

Patented May 4, 1926.

UNITED. STATES PATENT oFFlcE.

THOMAS'APPLEBY, or PHILADELPHIA, PENNSYLVANIA.

VARIABLE RESISTANCE.

Original application led March 23, 1920, Serial No. 368,046. Divided .and this application tiled November 26, 1923. serial N6. 677,163.

To a whom t may, concern.'

Be it`known that I, THOMAS APPLEBY, a citizen of the United States, residing in the city and county of Philadelphia, State of Pennsylvania, have invented certain new and useful Improvements in Variable Resistances, of which the following is a speciication.

My invention relates to rheostats or ad- 'ustable resistances continuously variable by infinitely small increments and utili-table, particularly when the resistance values are high, for eecting leakage paths in the eircuits of or between the electrodes of audions or similar devices utilized in radio systems, or for effecting coupling between circuits of co-operating audions.

It is characteristic of my invention that the resistance element consists of a conducting material, preferably of high speciic resistance and preferably non-meta lic such as graphite, deposited upon or applied to a non-conducting base or support by passing over the base or support, sufficiently rough for the purpose, in contact therewith a mass of the conducting material which in effect makes a pencil mark upon the support, the pencil mark constituting the resistance element and the conducting mass later coacting therewith constituting the movable contact of the rheostat.

This application is a division from my prior application Serial Number 368,046 filed March 23, 1920.

My invention resides in features of composition, structure and arrangement hereinafter described and claimed.

For an' illustration of some of the various forms my invention may take, reference is to be had to the accompanying drawing, in which:

Fig. 1 is a perspective view of one form' of my invention.

Figs. 2 and 3 are fragmentary elevational sections of apparatus of the character shown in Fig. 1.

Fig. 4 is a diagram of a radio system having my invention applied thereto.

'Fig 5 is a sectional view of a modification of my invention.

Fig. 6 is an elevational View of a portion of the apparatus of Fig. 5. L

Fig. 7 is a diagram of a further radio system in which my invention is applied.

As shown in Figs. 1, 2, and 3, a base 1 of non-conducting material such as hardl rubber, libre, moulding material such as bakellte or condensite, and the like, supports a' stationary interiorly threaded metal polst- 2, held by screw 3, and electrically connected to binding-post 5 by means of a metal strip 4. Rotatively mounted above post 2, by means of screw 3, is a knob 6 preferably of insulating material, to which .resilient`v positing a iilm or coating `1l (shown of ex- ,y

aggerated thickness) of its material on base 1 whenever drawn across the base by the rotation of knob 6. Contact 10 is of relatively low electrical resistance due to its size, but when its material is deposited in the form of a thin film or coating it forms 'a path of extremely high resistance. Film or coating 11 terminates in an enlarged portion 13 (shown of exaggerated thickness) which may be placed upon the base before bindingpost 12 is secured thereto and serves to make a relatively low resistance connection with the binding-post.

It will be understood that prior to the first rotative movement of knob 6, and excursion of Contact 10 across base 1, the resistance of the uncoated base between contact 10 and binding-post 12 is practically infinite, but as contact 10 is drawn across the base there will be deposited upon the base a thin film or coating 11 of the material of which the contact is composed, such as graphite for example, in much the same manner as a graphite line is drawn with an ordinary leadpencil. The film or coating thus applied will have a relatively high electrical resistance and continuous variation of this resistance bv infinitely small steps may be secured by shifting contact 10 to such position on film 11 as desired until a suitable value of resistance is obtained. 4Each successive excursion of contact 10 across base 1 will cause more of its material to be deposited on the base and thus the resistance of the film will, at,A least by a few traverses by Contact 10, be decreased. It will therefore be noted that the resistance element or film 11 has the unusual property of resistance decrease with deposited as before.

In Fig. 4 a radio antenna 15 is connected vto earth 16 through inductance 17 and tuning condenser 18. Enclosed in evacuated envelopef19 are anode 20, grid 21 and filament 22, comprisingone type of so called vacuumtube. The current for heating the filament,

and thus causing it to emit electrons, is fur,

nished by a battery 23 or any other convenient source of energy, and the anode or plate 2O is fed from direct current source 24 through a suitable translating device such as telephone-receivers 25; positive and negative terminals of this source are marked plus and minus respectively, in Fig. 4. Condenser 2'6 is serially connected in the grid circuit and its charges, and also those of grid 21, are permitted to leak away through variable resistance 27 which corresponds to Fig. 1. Instead of providing a path for the grid and grid condenser charges to leak away it has been found advantageous to the operation of some vacuum tubes to impress a. slight potential on the grid, as for eX- ample, grid 21 in) Fig. 4. For this purpose I may shunt grid condenser 26 with variable resistance 27 a to permit energy from source 24 to flow to the grid. It has also been found advantageous in radio and other circuits to' shunt condensers other than those of the grid with a variable leak resist-ance of the type herein described to prevent their retaining electrostatic charges for a longerA period than desired. In this respect I may also connect a variable resistance across the lates of antenna tuning condenser 18, or 1n shunt to any condenser used in radio or other electrical circuits. f

In the modification shown in Figs. 5 and 6, knob 28 of electrical insulating material, is rotatably mounted on an electrical nonconducting base or panel 29 by means of screw 31 and spring 32; a washer 30 may be placed between knob 28 and panel 29 to provide a bearing surface. Contact member 10 of graphite-or other suitable resistance material, slides longitudinally in tube or sleeve 33 and is firmly pressed against the inner side of knob 28 by means of a flat s ring 34; the fiat spring serving also to e ectri'cally connect the contact 10 with binding-post 35. Set screw 36 effectsptghe double purpose of locking the knob 28 to screw 31 and completing the electrical circuit from binding-post 37 lto washer 38, the washer being 1n contact with the enlarged portion 13 (see Fig. 6) ofresistance path 1l. It will be understood that as knob 28 isl rotated a portion of the material of which contact member 10 is com osed will be deposited o-n the inner side of t e knob ina similar manna 39 is connected to earth 40 through variv able tuning pondenser 41 and the primary coil 42 of radio frequency transformer 43. Secondary coil 44 is shunted by a variable tuning condenser 45 and one end connected through grid-condenser 46 to the grid elec-y trode 47 of an electron discharge device or vacuum tube whose electrodes are confined within evacuated envelope 48. The electron emitting filament 49 is heated by a battery or other source of energy 50 which flows through controllingmember or rheostat 51. Th-e other end of secondary coil 44 is connected to one side of the filament 49. A variable grid-leak 52 of the character herein disclosed is connected from the grid 47 to one side of filament 49 and serves to prevent the retention of undesirable charges on the grid 47 or in the grid-condenser 46. Energy for plate electro 'e 53/is furnished by a battery or other convenient source 55 the positive. terminal of which is connected through a controlling resistance 56, of the type disclosed, to plate electrode 53. The negative terminal of source 55 is connected to one side of filament 49. Interposed between plate electrode 53 of the first vacuum tube and grid 47 of the second vacuum tube is a second grid-condenser 46 which serves in part to lprevent energy from source 55 reaching the grid 47 of the second tube. This condenser performs the additional function of la by-pass for the radio frequency currents to grid 47 of the second tube, and the resistance of variable resistance 56 prevents these radio frequency currents from flowing to battery 55. The second vacuum tube shown in this circuit is similar to the first and similarly connected to the `same filament and plate batteries, with the exception that instead of a resist ance in the plate circuit there is interposed therein head-telephone 57, or other translating devices, and a condenser 58 which bypasses the radio frequency currents.

It will be understood that there is practically no limit to the number of steps of amplification that can be used and as many vacuum tubes as desired may be 'connected for this purpose in a similar manner to the two tubes shown in Fig. 7. The head-tele phone 57 and their shunting condenser 58 should always be connected to the last vacuum tube.

By actual test it was found Vthat man) vacuum tubes would properly function when used in connection with a variable grid-leak resistance or with a variable resistance coup- 1ing,whereas otherwise they were practicali 1y worthless due to the lack of a fixed resistance of proper value, although considerable experimentation with various xed re sistances had failed to disclose the proper value of the resistance required; theunsnccessf'ul results probably being due to the value of the resistance required being far from that of the resistance tried.

That I claim is:

1. A rheostat comprising a support of in-` sulating material, a movable contact of abradable resistance material, a movable conducting member supporting said contact and causing the same to engage and traverse said support to form thereon a resistance element consisting of material of said contact abraded therefrom, a xed circuit terminal connected with said contact through said conducting member, and a second fixed terminal having a fixed connection with said resistance element. w

2. A rheostat comprising a non-vitreous support of molded insulating material, a movable contact of abradable resistance material, a movable conducting lmember supporting said contact and causing the same to engage` and traverse said support to form thereon a resistance element consisting of material of said contactabraded therefrom, a fixed circuit terminal connected with said contact through said conducting member, and a second fixed terminal having a fixed connection with said resistance element.

3. A` rheostat comprising a movable contact member of abradable resistance material, a support engaged and traversed by Said movable contact member to form there-v on a resistance element of material abraded from said contact member, and conducting means having an exposed contacting surface of a width greater than the width of said resistance element and electrically connecting therewith. f

4. A rheostat vcomprising a movable contact member of abradable resistance material, a support vengaged and traversed by said -movable contactmember to form thereon a resistance element of material abraded j nection with said enlargement. f

6, A rheostit comprising a support, a movable contact member of abradable resistance material engaging with said support and adapted to traverse the same to deposit thereon a resistance element of said material abraded from said contact member, a pivoted conducting area carrying said contact member, a circuit connection with said area, and a fixed circuit connection electrically communicating at a fixed point with said resistance element.

7. A rheostat comprising a support of insulating material, a movable contact member of abradable resistance material, a mov-d able conducting member, means directly engaging said support for securing said conducting member to said support and said support carrying said contact member and causing the same to engage and traverse said support to form thereon a resistance element consisting of material of said contact member abraded therefrom, a fixed circuit terminal connected with said contact member through said conducting member, and a second fixed terminal having a fixed connection with said resistance element.

8. A rheostat comprising a support of insulating material, a movable contact member of abradable resistance material, a movable conducting member secured to said support and supporting said contact member and causing the same to engage and traverse said support to form directly on said support a resistance element consisting of material of said cont-act member abraded there l from, a circuit terminal connected with said contact member through said conducting member, and a fixed terminal having a fixed connection with said resistance element.

9. In a rheostat, a non-absorbent insulating base, two circuit terminals supported thereon, and means including a movable contact member of relatively soft conducting material supported on said base and electrically connected to one of said terminals to deposit a conductor upon said base between the other terminal and said contact member.

10. In a rheostat, a non-absorbent insulating base, two circuit terminals, supported thereon, and means including a movable graphite member supported on said Uase and electrically connected to one of said terminals to deposit aconductorl upon said base between the other terminal and said graphite member. a5

11. In a rheostat, a non-absorbent insulating base, two circuit terminals supported thereon, and means including a movable graphite pencil supported on said base and electrically connected to one of said terminals to deposit a conductor upon sai-d base between the other terminal and said graphite pencil. f

- nular strip, an arm attached tosaid pivot and extending radially over but separated from said strip, a sleeve supported on said arm above said strip, and a pencil shaped member supported in said sleeve andv in con-` tact with said strip to deposit a conducting coating upon said strip,

13. A rheostat comprising a non-absorbent insulating base. an annular high resistance unit mounted thereon., a pivoted arm mounted on said base and having a sleeve at the outer end, and an abradable contact member supported in Said sleeve to electrically conn'ect said high resistance unit, said arm .and` said contact.

14. A rheostat comprising a contact of abradable resistance material, 'a member lof insulating material, said member and contact being rotatable relatively to each other, a conducting member holding said contact in engagement with said member to form thereon a resistance element consisting of material of Said Contact abraded therefrom, a fixed circuit terminal connected with said contact through said conducting member, and a second ixed terminal connecting with said resistance element.

In testimony whereof I have hereunto athxedmy signature this 23rd dzy of N0- vember, 1923. l

' THOMAS APPLEBY. 

